The chemical vapor deposition (CVD)method is a film forming process frequently used in the semiconductor industry, wherein a liquid material is heated into a vapor reacting with special gases, and wherein the product then contacts and deposits on specified areas to form a film.
A considerable amount of waste gas is generated by the CVD process and needs processing by a detoxifier before exhaust. After cooling down, the waste gas will condense into corrosive dust. In order to avoid dust pollution and reduce the burden of the detoxifier, the dust is filtered beforehand.
Refer to FIG. 1 for a conventional dust collector. In order to filter out dust, let waste gas pass through a conventional dust collector 1. The conventional dust collector 1 has an inlet 2 and an outlet 3. Some separating boards 4 are arranged behind the inlet 2 to reduce backpressure and enable waste gas to enter the dust collector 1. A plurality of filter boards 5 is densely arranged before the outlet 3 to catch the dust generated by temperature drop as much as possible.
Refer to FIG. 2 and FIG. 3. In the conventional dust collector 1, a plurality of catch boards 6 is arranged between the inlet 2 and the outlet 3. The catch boards 6 respectively have different-size pores 7A, 7B, 7C, and 7D, whose diameters positively correlate with the distances between the catch boards 6 and the outlet 3. In other words, the closer the catch board 6 to the outlet 3, the smaller the diameter of the pores 7A, 7B, 7C, or 7D. The number of the pores 7A, 7B, 7C or 7D of a catch board 6 positively correlates with the distance between the catch board 6 and the inlet 2. In other words, the closer the catch board 6 to the inlet 2, the smaller the number of the pores 7A, 7B, 7C, or 7 of the catch board 6. The catch boards 6 may be roughly divided into a first region 8A and a second region 8B, wherein the first region 8A is nearer to the inlet 2. FIG. 2 schematically shows an overlapped view of the catch boards 6 in the first region 8A, wherein the pores 6A and 6B are larger. FIG. 3 schematically shows an overlapped view of the catch boards 6 in the second region 8B, wherein the pores 6C and 6D are obviously smaller.
Thereby, the dust carried by an air flow 9 will be caught by and deposits on the pores 7A, 7B, 7C, and 7D of the catch boards 6 after it enters the dust collector 1. Thus is reduced the burden of the waste gas processor.
However, the pores 7A, 7B, 7C, and 7D of the catch boards 6 overlap. Therefore, the dust of the waste gas can easily pass through the pores 7A, 7B, 7C, and 7D, and the waste gas only stays in the dust collector 5 for a short time. In fact, the pores 7A, 7B, 7C, and 7D can only catch a limited amount of dust, and most of the dust is accumulated on the filter boards 5. Thus is obviously decreased the service life of the dust collector 1. Consequently, the dust collector 1 needs cleaning and replacing frequently. Thus is prolonged the maintenance downtime, decreased the productivity, and increased the fabrication cost.